Magnetic tape cartridge

ABSTRACT

In a magnetic tape cartridge comprising a thin cartridge casing having flat upper and lower surfaces and a single reel which is housed in the cartridge casing for rotation and around which a magnetic tape is wound, island-like or point-like projections are provided at least three places of the lower surfaces of the cartridge casing near the leading edge and the trailing edge of the cartridge casing as viewed in the direction X of insertion of the magnetic tape cartridge in a recording and reproducing apparatus and recesses which are adapted to be engaged with the projections are provided on the upper surface of the cartridge casing so that, when a plurality of the magnetic tape cartridges are stacked, the projections and the recesses of the cartridge casings of magnetic tape cartridges which are just above and below each other are engaged with each other, whereby the magnetic tape cartridges are prevented from being displaced with respect to each other when a plurality of magnetic tape cartridges are stacked and the sliding resistance when the magnetic tape cartridge is inserted into a recording and reproducing apparatus is reduced.

This is a divisional of application Ser. No. 09/700,469 filed Nov. 15,2000; the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a one-reel magnetic tape cartridge for use ina computer or the like.

BACKGROUND OF THE INVENTION

As a backup medium for a computer memory, there has been known amagnetic tape cartridge comprising a thin rectangular cartridge casingformed of upper and lower halves fixed together by screws or the likeand a single reel which is housed in the cartridge casing for rotationand around which a magnetic tape is wound.

When such a magnetic tape cartridge is loaded in a recording andreproducing apparatus, a drive member of the apparatus is engaged withengagement teeth on the reel exposed through a circular opening formedon the lower half of the cartridge casing at the center thereof and themagnetic tape wound around the reel is drawn out from the cartridgecasing into a predetermined position on the tape running path by a tapedrawing mechanism of the apparatus, whereby read/write of data becomesfeasible.

In such magnetic tape cartridges, conventionally, a projection forstacking is formed on the upper surface of the cartridge casing of eachmagnetic tape cartridge and a recess for stacking is formed on the lowersurface of the cartridge casing of each magnetic tape cartridge so that,when a plurality of magnetic tape cartridges are stacked, the recess forstacking on one magnetic tape cartridge is engaged with the projectionfor stacking on the upper magnetic tape cartridge, whereby the relativeposition between the upper and lower magnetic tape cartridges is fixedso that a plurality of magnetic tape cartridges can be transported in astacked state.

Conventionally, the projection for stacking on the lower surface of thecartridge casing is generally in the form of a pair of protrusions whichextend in the direction of insertion of the magnetic tape cartridge intothe recording and reproducing apparatus on opposite sides of thecircular opening. This arrangement gives rise to a problem that theprotrusions are apt to warp and when they warp, the protrusion on eachmagnetic tape cartridge cannot be stably engaged with the engagementrecess of the lower magnetic tape cartridge when a plurality of magnetictape cartridges are stacked, whereby the magnetic tape cartridges becomeshaky.

Further, there has been also a problem that the protrusions increasesliding friction when the magnetic tape cartridge is inserted into therecording and reproducing apparatus.

In the magnetic tape cartridge, locator holes for locating the magnetictape cartridge with respect to the recording and reproducing apparatusare often provided in the bottom wall of the lower half of the cartridgecasing. In such a case, bosses each provided with a locator holeextending through the boss are formed on the bottom wall of the lowerhalf at its four corners together with bosses each provided with throughholes through which a screw for fastening together the upper and lowerhalves of the cartridge casing is inserted.

Further, a tape draw-out opening through which the magnetic tape in thecartridge casing is drawn out is formed in the side wall of thecartridge casing near one corner thereof, and a taper leader member isremovably held in a space open to the tape draw-out opening between thelower surface of the top wall of the upper half and the upper surface ofthe bottom wall of the lower half. Accordingly, the tape draw-outopening must be provided with a space for accommodating the tape leadermember, a space through which the magnetic tape runs and a space throughwhich a tape draw-out member on the recording and reproducing apparatusis given access to the tape leader member, which greatly limits thespace near the tape draw-out opening in which bosses can be provided.

Further, since a circular rib which coaxially surrounds the reel iserected from the upper surface of the bottom wall of the lower half, thespace near the tape draw-out opening in which bosses can be provided isfurther limited and accordingly, the bosses for the locator holes andthe screw holes and the circular rib must be provided in contact witheach other or close to each other.

However, when the bosses and the rib are formed in contact with eachother or close to each other, the part is locally thickened, which makesit difficult to keep a sufficient dimensional accuracy and geometricaccuracy of the locator holes when the cartridge casing is molded due tononuniform cooling in the mold and difference in shrinkage factor.Further, the bosses, the holes and the rib become apt to lean.

Further, when there exists a part at which the wall thickness isextremely large as compared with other parts, there arises fear thatsink marks and/or welding lines are generated on the inner surface ofthe locator hole and the locator hole is disabled from functioning as alocator.

Further, even in the case where the bosses and the rib are in contactwith each other but are simply close to each other, the part of the wallof the mold between parts which are close to each other is less apt tobe cooled as compared with other parts, and accordingly, it is difficultto keep a sufficient dimensional accuracy and geometric accuracy and thebosses, the holes and the rib become apt to lean.

Further, the magnetic tape cartridge is generally provided with a brakemember which locks the reel not to rotate when the magnetic tapecartridge is not being used and a coiled spring which urges the brakemember in the direction of the axis of rotation of the reel. Generallythe cartridge casing is formed by plastic injection molding. The urgingforce of the coiled spring can deform outward the top wall and/or thebottom wall of the cartridge casing. When the top wall and/or the bottomwall of the cartridge casing is deformed outward, the cartridge casingcan interfere with the reel to obstruct rotation of the reel, locationof the magnetic tape cartridge with respect to the recording andreproducing apparatus can become infeasible and/or stacking of themagnetic tape cartridges can be adversely affected.

In order to overcome these problems, the cartridge casing has beenformed by molding of a glass-fiber reinforced polycarbonate resin or thelike so that the rigidity of the cartridge casing is increased anddeformation of the cartridge casing is prevented.

However this approach has been disadvantageous in that the service lifeof the molds is shortened and wear of the bucket of the recording andreproducing apparatus is increased when the magnetic tape cartridge isloaded in or unloaded from the recording and reproducing apparatus. Thatis, use of glass fiber reinforcement is not preferred from theseviewpoints.

Though the plastic injection molding is useful as a technique foraccurately and efficiently forming products of a complicated shape, itgives rise to a problem that a gate mark is left on the surface of theproducts which can obstruct loading and unloading of the magnetic tapecartridge in and from the recording and reproducing apparatus and can beground to produce plastic grindings during loading and unloading of themagnetic tape cartridge depending on the position of the gate mark.

When a desired magnetic tape cartridge is taken out from a library andloaded in a recording and reproducing apparatus by a chucking machine orwhen the magnetic tape cartridge is taken out from the recording andreproducing apparatus and returned to the library by the chuckingmachine, the gate mark sometimes obstructs stable chucking of themagnetic tape cartridge.

Though these problems can be avoided by disposing the gate in a recessof the surface of the cartridge casing, flow of the resin near the gatebecomes low since the wall thickness near the gate becomes smaller dueto existence of the recess. As a result, uneven packing of resin isgenerated near the gate, the end of the flow (e.g., side walls) can sinkto deteriorate the dimensional accuracy and, at the worst, short moldingcan occur due to a poor packing pressure. Though these problems can beavoided by providing a plurality of gates, the approach adds to the costand is not advantageous.

Further, the problems can be avoided by providing a tunnel gate or aside gate on a side wall or the like of the cartridge casing. However,this approach is disadvantageous in that the length of the path overwhich the resin flows is elongated and the dimensional accuracy of theproduct deteriorates.

Further, an arcuate rib is formed on each corner of the upper half tosurround the reel. The ends of the arcuate rib merge into side walls ofthe upper half in tangential directions of the rib. Further, a corner ofthe upper half is often provided with a cutaway portion for preventingthe magnetic tape cartridge from being inserted into the recording andreproducing apparatus in a wrong direction. The cutaway portion isformed, for instance, from the upper surface of the top wall of theupper half halfway of the height of the side wall by cutting the cornerof the upper half in a shape like a triangle including a point near theintersection of the arcuate rib and the side wall.

In such a case, the part of the side wall near the intersection forms arecess at an upper part thereof while forming a thick wall portion at alower portion thereof. The thick wall portion is cooled slower than thesurrounding parts, which results in a sinkmark and/or lean in the partnear the intersection and a step on the surface to be mated with thecorresponding part of the lower half.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, a first object ofthe present invention is to provide a magnetic tape cartridge which canbe stably stacked with other magnetic tape cartridges and is low insliding friction when it is inserted into a recording and reproducingapparatus.

A second object of the present invention is to provide a magnetic tapecartridge which is provided with a boss provided with a locator holeextending through the boss and a boss provided with a through holethrough which a screw for fastening together the upper and lower halvesof the cartridge casing both formed near a tape draw-out opening throughwhich the magnetic tape in the cartridge casing is drawn out, and is yethigh both in dimensional accuracy and geometric accuracy of the locatorhole.

A third object of the present invention is to provide a magnetic tapecartridge which is rigid enough to prevent expansion or deformation ofthe cartridge casing by urging force of the spring which urges the brakemember and to ensure a sufficient clearance between the reel and thecartridge casing even if the cartridge casing is formed by molding of aplastic material without glass fiber.

A fourth object of the present invention is to provide a magnetic tapecartridge which can be formed by injection molding in such a manner thatfine geometric properties can be formed with a high dimensional accuracywith one gate for each product disposed in a position where the gatemark does not interfere with loading and unloading the magnetic tapecartridge in and from the recording and reproducing apparatus and withchucking of the magnetic tape cartridge when the magnetic tape cartridgeis taken out from and returned to a library.

A fifth object of the present invention is to provide a magnetic tapecartridge in which the aforesaid drawbacks inherent to the magnetic tapecartridge where an arcuate rib is formed on each corner of the cartridgecasing to surround the reel so that their ends merge into side walls ofthe cartridge casing in tangential directions of the rib and a cutawayportion for preventing the magnetic tape cartridge from being insertedinto the recording and reproducing apparatus in a wrong direction isformed on a corner of the cartridge casing can be effectively avoided.

BRIEF DESCRIPTIONS OF THE INVENTION

The first object of the present invention can be accomplished by amagnetic tape cartridge in accordance with a first aspect of the presentinvention characterized in that island-like or point-like projectionsare provided at least three places of one of the upper and lowersurfaces of the cartridge casing and recesses which are adapted to beengaged with the projections are provided on the other of the upper andlower surfaces of the cartridge casing so that, when a plurality of themagnetic tape cartridges are stacked, the projections and the recessesof the cartridge casings of magnetic tape cartridges which are justabove and below each other are engaged with each other to keep therelative position between the magnetic tape cartridges.

That is, when the island-like or point-like projections are provided onthe lower surface of the cartridge casing, the recesses are provided onthe upper surface of the cartridge casing, and conversely, when theisland-like or point-like projections are provided on the upper surfaceof the cartridge casing, the recesses are provided on the lower surfaceof the cartridge casing.

The expression “island-like projection” means a projection which isindependent of its surroundings and has a small certain area and theexpression “point-like projection” means a projection which isindependent of its surroundings and has a smaller certain area.

When the projections are provided on the lower surface of the cartridgecasing and the recesses are provided on the upper surface of thecartridge casing, it is preferred that the height of the projections beslightly larger than the depth of the recesses so that a slight gap isformed between the lower surface of the upper magnetic tape cartridgeand the upper surface of the lower magnetic tape cartridge when aplurality of magnetic tape cartridges stacked with the projections andthe recesses engaged with each other.

Further, it is preferred that each of the projections be formed at apredetermined distance d from the edge of the cartridge casing.

Further, it is preferred that the height t of the projections be largerthan the distance d.

Further, it is preferred that the projections be formed near the leadingedge and the trailing edge of the cartridge casing with respect to thedirection of insertion of the magnetic tape cartridge into the recordingand reproducing apparatus.

Further, it is preferred that the distance d of the projection from theleading edge or the trailing edge of the cartridge casing satisfies thecondition t<d≦0.15D, wherein t represents the height of each projection,and D represents the length of the cartridge casing as measured in thedirection of insertion of the magnetic tape cartridge into the recordingand reproducing apparatus.

In the case where the projections are provided on the lower surface ofthe cartridge casing, it is preferred that the projections be formedoutside the circular opening, formed in the lower surface of thecartridge casing at the center thereof, with respect to the directionperpendicular to the direction of insertion of the magnetic tapecartridge into the recording and reproducing apparatus.

In the magnetic tape cartridge in accordance with the first aspect ofthe present invention, since the projections for holding the magnetictape cartridges in place relative to each other, when a plurality ofmagnetic tape cartridges are stacked, are island-like or point-like andare very small in area, the sliding friction acting between the magnetictape cartridge and the recording and reproducing apparatus can bereduced. Further, unlike the conventional magnetic tape cartridge wherethe projections are in the form of protrusions, a stack of the magnetictape cartridges becoming shaky due to warpage of the projections can beavoided.

When the projections are formed near the leading edge and the trailingedge of the cartridge casing with respect to the direction of insertionof the magnetic tape cartridge into the recording and reproducingapparatus, the magnetic tape cartridges are stabilized when they arestacked. In this case, when each of the projections is formed at apredetermined distance from the edge of the cartridge casing, damage onthe projections when the magnetic tape cartridge is dropped can besuppressed.

In the case where the projections are provided on the lower surface ofthe cartridge casing, when the projections are formed outside thecircular opening, formed in the lower surface of the cartridge casing atthe center thereof, with respect to the direction perpendicular to thedirection of insertion of the magnetic tape cartridge into the recordingand reproducing apparatus, the drive member of the apparatus can beprevented from interfering with the projections, and at the same time,the magnetic tape cartridges are more stabilized when they are stacked.

The second object of the present invention can be accomplished by amagnetic tape cartridge in accordance with a second aspect of-thepresent invention characterized in that a first boss provided with alocator hole for locating the magnetic tape cartridge relative to arecording and reproducing apparatus when the magnetic tape cartridge isloaded in the recording and reproducing apparatus and a second bossprovided with a through hole through which a screw for fasteningtogether the upper and lower halves of the cartridge casing is insertedare erected in contact with each other or close to each other from theinner surface of the cartridge casing near a tape draw-out opening, andthe wall thickness of the first boss is smaller than the wall thicknessof the second boss.

In this case, it is preferred that the wall thickness of the first bossbe in the range of 0.5 to 0.8 times the wall thickness of the secondboss.

Further, in the case where a sliding door for opening and closing thetape draw-out opening is provided, it is preferred that the second bossbe provided on the outer peripheral surface thereof with a flat surfacewhich is in alignment with the inner edge of a sliding groove formed onthe cartridge casing so that the sliding door slides on the groove.

In the case where an arcuate rib coaxially surrounding the reel iserected from the inner surface of the cartridge casing, it is preferredthat the first and second bosses be apart from the rib.

In the magnetic tape cartridge in accordance with the second aspect ofthe present invention, since the first boss provided with the locatorhole is smaller in wall thickness than the second boss provided with athrough hole through which a screw for fastening together the upper andlower halves of the cartridge casing is inserted, the first boss iscooled faster than the second boss and accordingly the dimensionalaccuracy and the geometric accuracy of the locator hole can be moreeasily obtained.

When the second boss is provided on the outer peripheral surface thereofwith a flat surface which is in alignment with the inner edge of thedoor sliding groove formed on the cartridge casing, the second boss canbe formed at a sufficient distance from the first boss, and accordinglythe dimensional accuracy and the geometric accuracy of the through holecan be more easily obtained and at the same time, lean of the locatorhole can be prevented.

Further, in the case where an arcuate rib coaxially surrounding the reelis erected from the inner surface of the cartridge casing, thedimensional accuracy and the geometric accuracy of the through hole canbe obtained by forming the first and second bosses apart from the rib.

In the case where a boss provided with a locator hole is erected fromthe inner surface of the lower half of the cartridge casing near a tapedraw-out opening, it is preferred that the lower surface of the upperhalf of the cartridge casing be provided with a circular recess opposedto the boss. The circular recess can be used for locating the upper halfrelative to the lower half during assembly of the magnetic tapecartridge.

The third object of the present invention can be accomplished by amagnetic tape cartridge in accordance with a third aspect of the presentinvention characterized in that a pair of protrusions are provided oneach of the lower surface of the top wall of the upper half of thecartridge casing and the upper surface of the bottom wall of the lowerhalf of the cartridge casing to respectively extend along diagonal linesof the cartridge casing.

Each of the protrusions may be uniform in height substantially over itsentire length. In this case, it is preferred that the protrusion isabout 0.1 mm to 0.5 mm in height. Otherwise, the protrusion may becomelower toward the side walls of the cartridge casing at a predeterminedrate or stepwise.

By providing such protrusions, the cartridge casing can be rigid enoughto prevent expansion or deformation of the cartridge casing by urgingforce of the spring which urges the brake member and to ensure asufficient clearance between the reel and the cartridge casing even ifthe cartridge casing is formed by molding of a plastic material withoutglass fiber.

Instead of providing such protrusions, the top wall of the upper half ofthe cartridge casing and the bottom wall of the lower half of thecartridge casing may be formed so as to be thicker toward the centerthereof.

The fourth object of the present invention can be accomplished by amagnetic tape cartridge in accordance with a fourth aspect of thepresent invention characterized in that a thick wall portion is formedin one of the top wall of the upper half of the cartridge casing and thebottom wall of the lower half of the same and a gate for injectionmolding is provided in a recess formed on the outer surface of the thickwall portion.

It is preferred that the thick wall portion be formed in the top wall ofthe upper half of the cartridge casing at the center thereof and thegate for injection molding be provided in a recess formed on the outersurface of the thick wall portion.

The gate may be provided in a recess formed on the outer surface of theupper half or the lower half for a purpose other than that for providinga gate.

By providing the gate in a recess, the problems that the gate mark lefton the surface of the product obstructs loading and unloading of themagnetic tape cartridge in and from the recording and reproducingapparatus and the gate mark is ground to produce plastic grindings canbe avoided. Further, by providing the gate in a recess formed on theouter surface of a thick wall portion, flow of the resin becomes moresmooth, and especially when the gate is provided in a recess formed onthe outer surface of a thick wall portion formed in the top wall of theupper half of the cartridge casing at the center thereof, the length ofthe path over which the resin flows during injection molding can besubstantially uniform, and the thickness of the cartridge casing nearthe gate can be prevented from becoming thin even if the gate is formedin a recess.

In the case where a pair of locator holes for locating the magnetic tapecartridge with respect to the recording and reproducing apparatus areprovided on the bottom surface of the lower half of the cartridgecasing, the gate may be provided in a recess formed on the bottomsurface of the lower half in a region surrounded by a straight centerline which passes through the center of the bottom surface of the lowerhalf in parallel to the straight line joining the locator holes and apair of straight lines extending on the bottom surface of the lower halfthrough the respective locator holes in perpendicular to the centerline. In this case, especially when the gate is provided atsubstantially the same distance from the locator holes, the resin can beevenly supplied to both the locator holes from the gate and accordinglythe locator holes can be formed at a high accuracy.

Further, in the case where the projections for stacking are provided onthe bottom surface of the lower half, the gate may be provided in aregion on the trailing side of the projections with respect to thedirection of insertion of the magnetic tape cartridge into the recordingand reproducing apparatus.

In this case, since the region is not brought into contact with therecording and reproducing apparatus when the magnetic tape cartridge isloaded in and unloaded from the recording and reproducing apparatus, theproblems that the gate mark left on the surface of the product obstructsloading and unloading of the magnetic tape cartridge in and from therecording and reproducing apparatus and the gate mark is ground toproduce plastic grindings can be avoided without forming a recess.

The fifth object of the present invention can be accomplished by amagnetic-tape cartridge in accordance with a fifth aspect of the presentinvention comprising a cartridge casing formed by fixing togetherrectangular upper and lower halves, a single reel which is housed forrotation in the cartridge casing and around which a magnetic tape iswound, an arcuate rib which is formed on the cartridge casing tosurround the reel and an end of which intersects a side wall of theupper half or the lower half to form a thick wall portion near theintersection of the end of the arcuate rib and the side wall, a cutawayportion, for preventing the magnetic tape cartridge from being insertedinto the recording and reproducing apparatus in a wrong direction,formed on the outer surface of the upper half or the lower half at acorner thereof to extend from the upper surface of the upper half or thebottom surface of the lower half halfway of the height of the side wallin such a manner that it cuts the corner in a shape like a triangleincluding the vicinity of the intersections of the arcuate rib and theside walls and characterized in that a thickness reduction portion whichmakes the thickness of the side wall substantially uniform is formed onthe back side of the side wall near the intersection.

By forming a thickness reduction portion on the part adjacent to thecutaway portion in the direction of height of the side wall, thedifference in cooling rate can be substantially nullified near theintersection, whereby formation of a sinkmark and/or lean in the partnear the intersection is prevented and formation of a step on thesurface at which the upper and lower halves are mated is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing the arrangement of amagnetic tape cartridge in accordance with a first embodiment of thepresent invention,

FIG. 2 is a perspective view showing the cartridge casing of themagnetic tape cartridge shown in FIG. 1 with the lower surface directedupward,

FIG. 3 is a perspective view showing the cartridge casing of themagnetic tape cartridge shown in FIG. 1 with the upper surface directedupward,

FIG. 4A is a schematic plan view of the cartridge casing shown in FIGS.2 and 3,

FIG. 4B is a schematic bottom view of the cartridge casing shown inFIGS. 2 and 3,

FIG. 5 is an enlarged fragmentary cross-sectional view showing a pair ofcartridge casings shown in FIGS. 2 and 3 in a stacked state,

FIGS. 6A and 6B are views for illustrating how the projection forstacking impacts against the floor when the magnetic tape cartridgedrops to the floor,

FIGS. 7A and 7B are views for illustrating the base of determining thedistance between the projection for stacking and the edge of thecartridge casing,

FIGS. 8A and 8B are perspective views for illustrating preferred shapeof the projection for stacking,

FIG. 9A is an enlarged fragmentary plan view showing the insidestructure of the lower half of the cartridge casing,

FIG. 9B is a cross-sectional view taken along line A—A in FIG. 9A,

FIGS. 10 and 11 are enlarged fragmentary plan views of modifications ofthe lower half of the cartridge casing shown in FIGS. 9A and 9B,

FIG. 12A is an enlarged fragmentary plan view showing the insidestructure of a lower half different from that shown in FIGS. 9A and 9B,

FIG. 12B is a cross-sectional view taken along line B—B in FIG. 12A,

FIG. 13 is an enlarged fragmentary plan view of a modification of thelower half of the cartridge casing shown in FIG. 12A,

FIG. 14A is an enlarged fragmentary plan view showing the insidestructure of a lower half different from those shown in FIGS. 9A and 9Band 12A and 12B,

FIG. 14B is a cross-sectional view taken along line C—C in FIG. 14A,

FIGS. 15 and 16 are enlarged fragmentary plan views showing the insidestructure of lower halves different from those shown in FIGS. 9A and 9B,12A and 12B, and 14A and 14B,

FIG. 17 is a bottom view of the upper half,

FIG. 18 is a view showing the inside structure of the upper and lowerhalves provided with protrusions diagonally extending on the innersurface of the upper and lower halves,

FIG. 19 is a cross-sectional view taken along line X—X or Y—Y in FIG.18,

FIG. 20 is a view showing the inside structure of a modification of theupper and lower halves shown in FIG. 18,

FIG. 21 is a cross-sectional view taken along line Z—Z in FIG. 20,

FIG. 22 is a view showing the inside structure of another modificationof the upper and lower halves shown in FIG. 18,

FIG. 23 is a view showing the inside structure of still anothermodification of the upper and lower halves shown in FIG. 18,

FIG. 24 is a perspective view of the cartridge casing as viewed from theside of the upper half for illustrating the position of the gate forinjection molding,

FIG. 25 is a cross-sectional view taken along line S—S in FIG. 24,

FIG. 26 is a perspective view of the cartridge casing as viewed from theside of the lower half for illustrating the position of the gate forinjection molding,

FIG. 27 is a perspective view showing a cartridge casing provided with acutaway portion for preventing the magnetic tape cartridge from beinginserted in a wrong direction,

FIG. 28 is a fragmentary bottom view of the upper half of the cartridgecasing shown in FIG. 27 where no measure to prevent deformation of theside wall is taken,

FIG. 29A is a cross-sectional view taken along line A—A in FIG. 28,

FIG. 29B is a cross-sectional view taken along line B—B in FIG. 28,

FIG. 30 is a fragmentary bottom view of the upper half of the cartridgecasing shown in FIG. 27 where a measure to prevent deformation of theside wall is taken, and

FIG. 31 is a cross-sectional view taken along line B—B in FIG. 30.

PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings, hereinbelow.

FIG. 1 is an exploded perspective view showing the arrangement of amagnetic tape cartridge in accordance with a first embodiment of thepresent invention. As shown in FIG. 1, a magnetic tape cartridge 1 ofthis embodiment comprises a hard plastic cartridge casing 7 formed byfixing upper and lower halves 2 and 3, which are similar to each otherand rectangular in plan, by fasteners such as screws at their fourcorners. A single reel 4 around which a magnetic tape 20 is wound ishoused for rotation in the cartridge casing 7. A circular opening 13 isformed in the bottom wall of the lower half 3 at the center thereof. Anarcuate rib 32 which coaxially surrounds the reel 4 is formed on each ofthe upper surface of the bottom wall of the lower half 3 and the lowersurface of the top wall of the upper half 2 (only the rib 32 on thelower half 3 is shown in FIG. 1).

The reel 4 comprises a lower reel 5 and an upper reel 6 bonded together,for instance, by ultrasonic welding. The lower reel 5 comprises acylindrical reel hub 23 around which the magnetic tape 20 is wound and aflange 24 which extends radially outward from the lower peripheral endof the reel hub 23 and integrally formed by molding of synthetic resin.A reel plate 8 which is magnetically engaged with a reel drive means forrotating the reel 4 is mounted on the outer surface of the bottom of thereel hub 23. A brake gear 23A is formed on the inner surface of thebottom of the reel hub 23. The brake gear 23A is adapted to be engagedwith a break gear 9A formed on a brake button 9 to prevent rotation ofthe reel 4 when the magnetic tape cartridge 1 is not being used. Thereel hub 23 is provided with an opening 23B through which a brakerelease spindle of a recording and reproducing apparatus pushes upwardthe brake button 9.

The brake button 9 is provided with the brake gear 9A on the sideopposed to the reel hub 23, and an engagement groove 9B into which abrake guide projection on the upper half 2 is inserted is formed on theside of the brake button 9 opposite to the brake gear 9A. The brakebutton 9 is incorporated in the reel hub 23 urged downward by a coiledspring 10, whereby the brake gear 9A of the brake button 9 and the breakgear 23A of the reel hub 23 are normally in mesh with each other toprevent rotation of the reel 4. When the magnetic tape cartridge 1 isloaded in the recording and reproducing apparatus, the brake releasespindle of the recording and reproducing apparatus moves upward thebrake button 9 overcoming the force of the coiled spring 10 to releasethe brake gear 9A from the brake gear 23A, thereby permitting rotationof the reel 4.

In one side wall of the cartridge casing 7, a tape draw-out opening 26through which the magnetic tape 20 is drawn out is formed. The tapedraw-out opening 26 is opened and closed by a sliding door 27 which ismovable back and forth in parallel to the side wall as shown bydouble-headed arrow A. The sliding door 27 is spring-urged in theclosing position and normally held there.

When the magnetic tape cartridge 1 is not being used, the magnetic tape20 is fully taken up around the reel 4, where a leader member 21 in theform of a pin (for introducing the magnetic tape 20 into the taperunning path in the recording and reproducing apparatus) is held by aholding member in a recess 28 formed near the tape draw-out opening 26.

When the magnetic tape cartridge 1 is loaded in the recording andreproducing apparatus, the brake gear 9A of the brake button 9 isreleased from the brake gear 23A of the reel hub 23 to permit the reel 4to rotate, and at the same time, the reel drive means is magneticallyengaged with the reel plate 8 to rotate the reel 4. At the same time,the sliding door 27 is opened and the leader member 21 is introducedinto a predetermined position on the tape running path, wherebyread/write of data from and on the magnetic tape 20 becomes feasible.

A noncontacting memory 30 for recording contents or the like ofinformation recorded on the magnetic tape 20 is mounted in a corner 7Aof the cartridge casing 7. The noncontacting memory 30 is a rectangularplate-like member in which read/write of information can be effectedwithout contacting the memory 30, for instance, by electromagneticinduction. The noncontacting memory 30 is supported in the cartridgecasing 7 so that the read/write means of the recording and reproducingapparatus can easily effect read/write.

FIG. 2 is a perspective view showing the cartridge casing 7 with thelower surface directed upward, FIG. 3 is a perspective view showing thecartridge casing 7 with the upper surface directed upward, FIG. 4A is aschematic plan view of the cartridge casing 7, and FIG. 4B is aschematic bottom view of the cartridge casing 7.

The cartridge casing 7 is provided with flat upper and lower surfaces 7a and 7 b. As clearly shown in FIG. 3, the tape draw-out opening 26through the end of the magnetic tape 20 is drawn out is formed in theside wall of the cartridge casing 7 to extend from the lower half 3 tothe upper half 2, and the sliding door 27 closes and opens the opening26. As described above, the sliding door 27 is urged toward the closingposition and held there by a spring (not shown) built in the cartridgecasing 7. The leader member 21 in the form of a pin clamping the end ofthe magnetic tape 21 (FIG. 1) is removably held inside the tapedrawn-out opening 27.

The cartridge casing 7 is inserted into the recording and reproducingapparatus in the direction of arrow X in FIGS. 2, 3 and 4B, and isprovided on its trailing end face with a labeling region 7 c to which alabel is applied. The circular opening 13 is formed at the center of thelower half 3.

As shown in FIGS. 2 and 4B, the lower surface 7 b of the cartridgecasing 7 is provided with four island-like or point-like stackingprojections 11. The stacking projections 11 are for preventing themagnetic tape cartridges 1 from being displaced from each other when aplurality of magnetic tape cartridges 1 are stacked and are disposedsymmetrically with respect to both the horizontal and vertical linespassing through the center of the circular opening 13. As shown in FIGS.3 and 4A, the upper surface 7 a of the cartridge casing 7 is providedwith four recesses 12 which adapted to be engaged with the stackingprojections 11 of the upper magnetic tape cartridge 1 when a pluralityof magnetic tape cartridges are stacked. Each of the recesses 12 alsoopen to the side surfaces of the cartridge casing 7. Though theillustrated projection 11 are substantially rectangular in plan, theymay be square or circular in plan.

In order to prevent the stacking projections 11 from interfering withthe reel drive means of the recording and reproducing apparatus when thereel drive means accesses the magnetic tape cartridge 1, it is preferredthat the projections 11 be positioned so that the lines L1 and L2 (FIG.4B) which pass the inner edges of the projections 11 in parallel to thedirection of insertion of the magnetic tape cartridge 1 lie outside thecircular opening 13.

As shown in FIG. 5, showing a pair of cartridge casings 7 in a stackedstate, it is preferred that the height t of the projections 11 on thelower surface 7 b of the cartridge casing 7 be slightly larger than thedepth of the recesses 12 on the upper surface 7 a of the cartridgecasing 7 so that a slight gap G is formed between the lower surface 7 bof the upper cartridge casing 7 and the upper surface 7 a of the lowercartridge casing 7 when a plurality of magnetic tape cartridges 1 arestacked. With this arrangement, the lower surface 7 b of the uppercartridge casing 7 and the upper surface 7 a of the lower cartridgecasing 7 do not scrape against each other when a plurality of magnetictape cartridges 7 are transported in a stacked state, whereby generationof powder of the material due to wear, which can cause drop-out can beprevented and at the same time, the upper surfaces 7 a or the lowersurfaces 7 b of the cartridge casings 7 can be prevented from beingscratched.

Further, it is preferred that the projections 11 be formed near theleading edge or the trailing edge of the cartridge casing 7 (the upperand lower edges as seen in FIG. 4B) from the viewpoint of stability ofstacked magnetic tape cartridges 1. However, in the case where theprojections 11 are formed in contact with the edges, the projections 11impact against the floor F as shown in FIG. 6A and can be collapsed whenthe magnetic tape cartridge 1 obliquely drops to the floor F, wherebythe projections 11 is disabled from engaging with the recesses 12.Further, when the mold for molding the cartridge casing 7 is formed sothat the projections 11 are formed in contact with the edges, marks ofprocessing machines (e.g., cutting marks or spark erosion marks) areleft on the side surface of the projections 11, which makes it difficultto make the mold.

In order to avoid this problem, in this particular embodiment, theprojections 11 are formed at a predetermined distance d from the edgesof the cartridge casing 7 as shown in FIG. 5. It is preferred that thedistance d be larger than the height t of the projections 11 so thatfear of collapse of the projections 11 is reduced when the magnetic tapecartridge 1 drops to the floor F as shown in FIG. 6B.

FIGS. 7A and 7B are views for illustrating the base of determining thedistance d between the projections 11 and the leading and trailing edgesof the cartridge casing 7 taking into account warpage of the cartridgecasing 7 (exaggerated in FIGS. 7A and 7B). That is, assuming that

(1) the warpage of the cartridge casing 7 is in a quadric curve,

(2) an acceptable warpage of the cartridge casing 7 is 0.2 mm for eachside, and

(3) the height of the effective portion of the projections is 0.2 mm,

and the length of the cartridge casing 7 in the direction of insertionis D, it is preferred that formula t<d≦0.15D be satisfied.

In order to facilitate engagement of the projections 11 with therecesses 12, it is preferred that the edges of the projections 11 berounded as shown in FIG. 8A or the side surfaces of the projection 11 beinclined. Further when the edge of the cartridge casing 7 near to theprojection 11 is rounded, it is preferred that the projection 11 beapart from the rounded portion.

As can be understood from the description above, in this embodiment,since island-like or point-like projections 11 are formed on the lowersurface 7 b of the cartridge casing 7 so that when a plurality ofmagnetic tape cartridges 1 are stacked, the projections 11 on eachmagnetic tape cartridge 1 are engaged with recesses 12 formed on theupper surface 7 a of the lower magnetic tape cartridge 1 and the stackof the magnetic tape cartridges is stabilized, the sliding resistancewhen the magnetic tape cartridge 1 is inserted into a recording andreproducing apparatus can be reduced. Further, unlike the conventionalmagnetic tape cartridges where the projections are in the form ofprotrusions, a stack of the magnetic tape cartridges becoming shaky dueto warpage of the projections can be avoided.

Since the projections 11 are positioned near the leading edge and thetrailing edge of the cartridge casing 7 in the direction of insertion ofthe magnetic tape cartridge 1 and positioned in the directionperpendicular to the direction of insertion of the magnetic tapecartridge 1 so that the lines L1 and L2 (FIG. 4B) which pass the inneredges of the projections 11 in parallel to the direction of insertion ofthe magnetic tape cartridge 1 lie outside the circular opening 13, thestack of the magnetic tape cartridges 1 is stabilized and at the sametime, the stacking projections 11 are prevented from interfering withthe reel drive means of the recording and reproducing apparatus when thereel drive means accesses the magnetic tape cartridge 1.

Further, when formula t<d≦0.15D, wherein d represents the distancebetween the projections 11 and the leading and trailing edges of thecartridge casing 7, t represents the height of the projections 11 and Drepresents the length of the cartridge casing 7 in the direction ofinsertion, is satisfied, the stack of the magnetic tape cartridges 1 isstabilized and at the same time, damage on the projections 11 can beprevented when the magnetic tape cartridge 1 drops.

Though, in the embodiment described above, the projections 11 areprovided on the lower surface 7 b of the cartridge casing 7 and therecesses 12 are provided on the upper surface 7 a of the cartridgecasing 7, the projections 11 may be provided on the upper surface 7 a ofthe cartridge casing 7 and the recesses 12 are provided on the lowersurface 7 b of the cartridge casing 7. Also in this case, the distance dmay be set in the similar manner taking into account the warpage of thecartridge casing 7 such as shown in FIG. 7B.

In order to keep stability of the stack of the magnetic tape cartridges,the projections 11 may be three in number. Accordingly, only oneprojection 11 may be formed near the trailing edge of the cartridgecasing 7. Further, though, in the embodiment described above, the tapedraw-out opening 26 is closed and opened by the sliding door 27, theopening 26 may be provided with a different type of door.

The tape draw-out opening 26 must be provided with a space foraccommodating the tape leader member 21, a space through which themagnetic tape 20 runs and a space through which a tape draw-out memberon the recording and reproducing apparatus is given access to the tapeleader member 21, which greatly limits the space near the tape draw-outopening 26 in which bosses can be provided.

Further, since the circular rib 32 (FIG. 1) which coaxially surroundsthe reel 4 is erected from the upper surface of the bottom wall of thelower half 3, the space near the tape draw-out opening 26 in whichbosses can be provided is further limited and accordingly, the bossesfor the locator holes for locating the magnetic tape cartridge 1 withrespect to the recording and reproducing apparatus and for the screwholes for fixing the upper and lower halves and/or the circular rib mustbe provided in contact with each other or close to each other.

However, when the bosses and the rib are formed in contact with eachother or close to each other, the part is locally thickened, which makesit difficult to keep a sufficient dimensional accuracy and geometricaccuracy of the locator holes when the cartridge casing is molded due tononuniform cooling in the mold and difference in shrinkage factor due tothe thickness difference. Further, the bosses, the holes and the ribbecome apt to lean.

Further, when there exists a part at which the wall thickness isextremely large as compared with other parts, there arises fear thatsink marks and/or welding lines are generated on the inner surface ofthe locator hole and the locator hole is disabled from functioning as alocator.

Further, even in the case where the bosses and the rib are in contactwith each other but are simply close to each other, the part of the wallof the mold between parts which are close to each other is less apt tobe cooled as compared with other parts, and accordingly, it is difficultto keep a sufficient dimensional accuracy and geometric accuracy and thebosses, the holes and the rib become apt to lean.

FIGS. 9 to 16 show structures which can ensure the dimensional accuracyand the geometric accuracy even if a boss provided with a locator holeis formed near the tape draw-out opening close to a boss provided with ascrew hole for a screw for fixing the upper and lower halves.

FIG. 9A is an enlarged fragmentary plan view showing the insidestructure of the lower half of the cartridge casing, and FIG. 9B is across-sectional view taken along line A—A in FIG. 9A.

An end portion of a side wall 3 a of the lower half 3 is cut to form thetape draw-out opening 26, and a recess 28 which removably holds thelower end portion of the leader member 21 (FIG. 1) is formed on theupper surface 3 b of the bottom wall of the lower half 3 to open to thetape draw-out opening 26 (a similar recess is formed also on the lowersurface of the top wall of the upper half 2). Further, a sliding groove31 on which the sliding door 27 slides is formed inside the side wall 3a to extend along the inner surface of the side wall 3 a across therecess 28. From the upper surface 3 b of the bottom wall of the lowerhalf, is erected a circular rib 32 to coaxially surround the reel 4.

A boss 34 (a first boss) provided with a locator hole (a blind hole) 33which is coaxial with the boss 34 and opens on the lower surface 3 c ofthe bottom wall of the lower half 3 is erected from the upper surface 3b of the bottom wall of the lower half 3 integrated with an end of therib 32. Further, a boss 36 (a second boss) which is provided with ascrew hole (a through hole) 35 coaxially therewith is erected on theside of the boss 34 nearer to the tape draw-out hole 26 integrated withboth the boss 34 and the rib 32. The lower end portion 35 a of the screwhole 35 at which the screw hole 35 opens on the lower surface 3 c of thebottom wall of the lower half 3 is of a larger diameter to accommodatethe head of a screw for fixing the upper and lower halves 2 and 3. Aself-tapping screw is inserted into the screw hole 35 from the lowersurface 3 c so that the leading end portion of the screw is inserted ina self-tapping fashion into a hole formed in a boss (not shown) erectedfrom the lower surface of the top wall of the upper half 2 and fasteningtogether the upper and lower halves 2 and 3.

The wall thickness t1 of the boss 34 provided with the locator hole 33is smaller than the wall thickness t2 of the boss 36, the wall thicknesst3 of the rib 32 or the sum of the wall thicknesses t2 and t3. It ispreferred that the wall thickness t1 be smaller than the wall thicknesst4 of the bottom wall of the lower half 3. It is further preferred thatthe wall thickness t1 of the boss 34 be 0.5 to 0.8 times the wallthickness t2, t3 and t4. Further, it is preferred that the wallthickness of the boss 34 be smaller than the thickness of the otherparts at least over its entire circumference.

When the wall thickness t1 of the boss 34 provided with the locator hole33 is smaller than the wall thickness of the other parts, the boss 34 iscooled and solidified faster than the other parts and accordingly thedimensional accuracy and the geometric accuracy of the locator hole 33can be more easily obtained.

The structure shown in FIG. 10 is a modification of the structure shownin FIG. 9A and in the structure shown in FIG. 10, the locator hole 33 inthe boss 34 is substantially square whereas the locator hole 33 in theboss 34 is circular in the structure shown in FIG. 9A. The locator hole33 may be of a hexagon or other polygon in shape. Also, the boss 34itself may be substantially square.

In the structure shown in FIG. 11, the bosses 34 and 36 and the rib 32are joined together and a recess 37 is formed on the inner surface ofthe rib 32 at the joint. Also with this arrangement, the effect similarto that obtained by the aforesaid structures can be obtained.

FIGS. 12A and 12B show still another structure of this part. FIG. 12A isan enlarged fragmentary plan view showing the inside structure of alower half different from those described above, and FIG. 12B is across-sectional view taken along line B—B in FIG. 12A.

In this structure, the end portion of the rib 32 is shortened and isapart from the boss 34 provided with the locator hole 33. Also with thisarrangement, the effect similar to that obtained by the structure shownin FIG. 11 where the recess 37 is formed can be obtained. The structureshown in FIG. 13 is a modification of the structure shown in FIG. 12Aand in the structure shown in FIG. 13, the locator hole 33 in the boss34 is substantially square whereas the locator hole 33 in the boss 34 iscircular in the structure shown in FIG. 12A.

In the structures shown in FIGS. 9 to 13, the boss 36 provided with thescrew hole 35 is formed close to the boss 34 provided with the locatorhole 33 and the bosses 34 and 36 are joined together. In this case,though the door for closing the tape draw-out opening 26 need not belimited to the sliding door 27, the door is normally in the form of thesliding door. Still other structures are shown in FIGS. 14 to 16.

In the structure shown in FIGS. 14A and 14B, which are an enlargedfragmentary plan of the lower half and a cross-sectional view takenalong line C—C in FIG. 14A, the boss 34 provided with the locator hole33 and the boss 36 provided with the screw hole 35 are joined with therib 32 apart from each other. Accordingly, the boss 36 is displacedtoward the sliding groove 31 for the sliding door 27 and is formed witha flat surface 36 a in alignment with the inner edge 31 a of the slidinggroove 31. In other words, the outer peripheral surface of the boss 36is cut in a D-shape. Further, the wall thickness of the boss 34 issmaller than that of the boss 36.

With this arrangement, the boss 36 can be erected at a sufficientdistance from the boss 34, and accordingly, a sufficient dimensionalaccuracy and a sufficient geometric accuracy of the locator hole 33 canbe ensured and at the same time, lean of the locator hole 33 can beprevented.

In the structure shown in FIG. 15, the boss 36 is formed with a flatsurface 36 a in alignment with the inner edge 31 a of the sliding groove31 as in the structure shown in FIG. 14A. However, in the structureshown in FIG. 15, both the bosses 34 and 36 are formed apart from therib 32. Further, in the structure shown in FIG. 16, in addition to thefeature shown in FIG. 15, the locator hole 33 is substantially squareand the outer peripheral surface of the boss 34 is cut in a D-shape.

The locator holes 33 may be used not only to locate the magnetic tapecartridge 1 when the magnetic tape cartridge 1 is loaded in a recordingand reproducing apparatus but also to locate the lower half 3 in theautomatic assembly of the magnetic tape cartridge 1.

FIG. 17 is a bottom view showing the upper half 2 to be mated with thelower half 3 partly abbreviated. As shown in FIG. 17, on the back sideof the upper half 2, arcuate ribs 32 which coaxially surround the reel 4are provided, bosses 36′, into which the screws for fastening the upperand lower halves 2 and 3 are inserted in a self-tapping fashion, areprovided to be opposed to the bosses 36 on the lower half 3, and a pairof circular recesses 38 are provided to be opposed to the bosses 34provided with the locator holes 33 on the lower half 3. The recesses 38may be used to locate the upper half 2 in the automatic assembly of themagnetic tape cartridge 1.

The cartridge casings 7 with the structure described above are generallyformed by injection molding. There has been a problem that the top walland the bottom wall of the cartridge casing 7 are sometimes deformed(expanded) outward by the force of the coiled spring 10 (FIG. 1) in thecartridge casing 7. Such deformation of the top wall and the bottom wallsometimes gives rise to a problem that the cartridge casing 7 interfereswith the reel 4 to obstruct rotation of the reel 4 when the magnetictape cartridge 1 is loaded in a recording and reproducing apparatus, themagnetic tape cartridge 1 cannot be located or the magnetic tapecartridges 1 cannot be properly stacked.

In order to overcome such a problem, conventionally the cartridge casing7 has been formed by molding of a hard resin such as a glass-fiberreinforced polycarbonate resin so that the rigidity of the cartridgecasing is increased and deformation of the cartridge casing 7 isprevented.

However this approach has been disadvantageous in that the service lifeof the molds is shortened and wear of the bucket of the recording andreproducing apparatus is increased when the magnetic tape cartridge 1 isloaded in or unloaded from the recording and reproducing apparatus. Thatis, use of glass fiber reinforcement is not preferred from theseviewpoints.

In the cartridge casings shown in FIGS. 18 to 23, a pair of protrusions40 are provided on each of the lower surface 2 b of the top wall 2A ofthe upper half 2 of the cartridge casing 7 and the upper surface 3 b ofthe bottom wall 3A of the lower half 3 of the cartridge casing 7 torespectively extend along diagonal lines of the cartridge casing 7,whereby the cartridge casing 7 can be rigid enough to prevent expansionor deformation of the cartridge casing 7 by urging force of the coiledspring 10 and to ensure a sufficient clearance between the reel 4 andthe cartridge casing 7 even if the cartridge casing 7 is formed bymolding of a hard resin without glass fiber.

FIG. 18 is a view showing the inside structure of the upper and lowerhalves 2 and 3, FIG. 19 is a cross-sectional view taken along line X—Xor Y—Y in FIG. 18, FIG. 20 is a view showing the inside structure of amodification of the upper and lower halves 2 and 3 shown in FIG. 18,FIG. 21 is a cross-sectional view taken along line Z—Z in FIG. 20, FIG.22 is a view showing the inside structure of another modification of theupper and lower halves 2 and 3 shown in FIG. 18, and FIG. 23 is a viewshowing the inside structure of still another modification of the upperand lower halves 2 and 3 shown in FIG. 18.

The protrusions 40 may extend full to the corners of the upper and lowerhalves 2 and 3 as shown in FIG. 18. However, another component, e.g., amemory 30 shown in FIG. 1, is sometimes disposed in the space defined bythe side walls 2 a and 3 a of the upper and lower halves 2 and 3 and thearcuate rib 32 surrounding the reel 4. In such a case, the protrusions40 are formed only inside the arcuate rib 32 as shown in FIG. 20. Thoughprojections 44 formed on the brake button 9 to prevent rotation of thebrake button 9 and an annular rib 46 around the projections 44 are shownin FIG. 20, the projections 44 are abbreviated in FIGS. 18 and 22.

As shown in FIG. 19, the height t₅ of the protrusions 40 is about 0.1 to0.5 mm. The height of the protrusions 40 may be uniform over the entirelength thereof. However, since wobble of the reel 4 is larger toward theperipheral edge of the reel 4, the clearance between the reel 4 and thelower surface 2 b of the top wall 2A of the upper half 2 and theclearance between the reel 4 and the upper surface 3 b of the bottomwall 3A of the lower half 3 are smaller at the portion near the sidewalls 2 a and 3 a than at the portion near the center of the top wall 2Aand the bottom wall 3A, and accordingly, the reel 4 can interfere withthe protrusions 40 at the portion near the side walls 2 a and 3 a. Insuch a case, it is preferred that the height t₅ of the protrusions 40 bereduced toward the side walls 2 a and 3 a as shown in FIG. 21. At thistime, the height t₅ of the protrusions 40 may be gradually reduced at apredetermined rate or reduced stepwise.

Further, though, in FIGS. 18 and 20, a single protrusion 40 extendsalong each of the diagonals, a pair of protrusions may be provided alongeach of the diagonals to extend in parallel to each other. Further, apair of protrusions 41 and 42 which are respectively parallel to theside walls of the cartridge casing 7 may be formed on each of the upperand lower halves 2 and 3 to extend radially in addition to theprotrusions 40 extending along the diagonals as shown in FIG. 22.Further, though it is possible to form four protrusions which do notextend through the center of the cartridge casing 7 and extend to form asquare, it is preferred that the protrusions extend radially passingthrough the center of the cartridge casing 7 in order to uniform theflow of the resin in injection molding of the cartridge casing 7.Further, when two or more pairs of protrusions are provided as shown inFIG. 22, the rigidity of the cartridge casing 7 can be sufficient evenif the width of each protrusion is smaller as compared with when only apair of protrusions are provided.

Further, instead of providing such protrusions, the rigidity of thecartridge casing 7 may be increased by making larger the thickness ofthe top wall 2A of the upper half 2 and the bottom wall 3A of the lowerhalf 3 toward the center of the cartridge casing 7 as shown in FIG. 23.In this case, if the thickness t₆ of the top wall 2A near the arcuaterib 32 or the bottom wall 3A near the arcuate rib 32 is small, sinkmarksare generated on the surface of the half opposed to the arcuate rib 32after cooling. In order to suppress the sinkmarks, it is preferred thatthe wall thickness t₆ near the arcuate rib 32 be larger than thethickness t₇ of the side walls 2 a and 3 a. In order to suppressdeformation of the cartridge casing 7 and to increase the impactstrength of the cartridge casing 7, it is preferred that the corners 43formed by the side walls 2 a and 3 a, the top wall 2A and the bottomwall 3A be rounded.

The cartridge casing 7 is generally formed by plastic injection moldingas described above. Problems which are involved by the injection moldingwill be described, hereinbelow.

When the magnetic tape cartridge 1 is loaded in the recording andreproducing apparatus, the magnetic tape cartridge 1 is located withrespect to the recording and reproducing apparatus on the basis of thelocator holes 33 formed in the bottom wall of the cartridge casing 7(FIGS. 9A and 9B), the outer surface of the cartridge casing 7 itself orthe like. The magnetic tape cartridges 1 are sometimes arranged in alibrary. In order to prevent the magnetic tape cartridges 1 from beingdisplaced from each other, the aforesaid projections 11 and the recesses12 are formed on the cartridge casing 7 as shown in FIGS. 2 and 3. Adesired magnetic tape cartridge 1 is taken out from the library andloaded in a recording and reproducing apparatus.

The injection molding is a very important technique which can formproducts of a complicated shape with a high dimensional accuracy at ahigh efficiency. However, the injection molding gives rise to a problemthat a gate mark is left on the surface of the products which canobstruct loading and unloading of the magnetic tape cartridge 1 in andfrom the recording and reproducing apparatus and can be ground toproduce plastic grindings during loading and unloading of the magnetictape cartridge 1 depending on the position of the gate mark.

When a desired magnetic tape cartridge 1 is taken out from a library andloaded in a recording and reproducing apparatus by a chucking machine orwhen the magnetic tape cartridge 1 is taken out from the recording andreproducing apparatus and returned to the library by the chuckingmachine, the gate mark sometimes obstructs stable chucking of themagnetic tape cartridge.

Though these problems can be avoided by disposing the gate in a recessof the surface of the cartridge casing 7, flow of the resin near thegate becomes low since the wall thickness near the gate becomes smallerdue to existence of the recess. As a result, uneven packing of resin isgenerated near the gate, the end of the flow (e.g., side walls) can sinkto deteriorate the dimensional accuracy and, at the worst, short moldingcan occur due to a poor packing pressure. Though these problems can beavoided by providing a plurality of gates, the approach adds to the costand is not advantageous.

Further, the problems can be avoided by providing a tunnel gate or aside gate on a side wall or the like of the cartridge casing. However,this approach is disadvantageous in that the length of the path overwhich the resin flows is elongated and the dimensional accuracy of theproduct deteriorates.

A magnetic tape cartridge which can be formed by injection molding insuch a manner that fine geometric properties can be formed with a highdimensional accuracy with a single gate for each product disposed in aposition where the gate mark does not interfere with loading andunloading the cartridge casing 7 in and from the recording andreproducing apparatus and with chucking of the cartridge casing 7 whenthe magnetic tape cartridge is taken out from and returned to a librarywill be described hereinbelow.

FIG. 24 is a perspective view showing an appearance of a cartridgecasing 7 as viewed from the side of the upper half 2, FIG. 25 is across-sectional view taken along line S—S in FIGS. 20 and 24, and FIG.25 is a perspective view showing an appearance of the cartridge casing 7as viewed from the side of the lower half 3.

As shown in FIGS. 20 and 21, four projections 44 are erected from thelower surface of the top wall 2A of the upper half 2 at the centerthereof, the part of the top wall 2A on which the projections 44 areformed and the part of the top wall 2A surrounded by the projections 44are thickened to form a thick wall portion 45 whose wall thickness islarger than the base wall thickness to of the top wall 2A as shown inFIG. 25. Further, annular rib 46 is formed to surround the projections44, and the part of the top wall 2A on which the annular rib 46 isformed is also thickened to form a thick wall portion 47 whose wallthickness is larger than the base wall thickness to of the top wall 2A.A recess 48 is formed on the outer surface of the central thick wallportion 45 of the top wall 2A at the center thereof indicated by arrow A(the center of the thick wall portion 45 is also the center of the topwall 2A), and a gate for injection molding is formed in the recess 48.

The recess 48 in which the gate is formed may be formed in any positionon the outer surface of the thick wall portion at the center of the topwall 2A without being limited to the position indicated by arrow A. Forexample, the recess 48 may be formed in an area (indicated by arrow B)near to the tape draw-out opening 26 on the outer surface of the thickwall portion 47 formed by the rib 46 (an area nearer to the opening 26than the center of the top wall 2A).

When the gate is provided in the recess 48 formed on the outer surfaceof the thick wall portion at the center of the top wall 2A, the pathalong which the resin flows during injection molding of the upper half 2can be uniformed since the gate is positioned at the center of the topwall 2A. Further, since the gate is in the recess 48, the gate markcannot obstruct loading and unloading of the magnetic tape cartridge 1in and from the recording and reproducing apparatus and taking out themagnetic tape cartridge 1 from and returning the same to a library.Further, since the recess 48 is formed in the thick wall portion, thewall thickness in the vicinity of the gate can be larger as comparedwith when the gate is formed in a portion other than a thick wallportion, whereby deterioration in flowability of the resin near the gatecan be avoided.

When the recess 48 is formed in a position near the tape draw-outopening 26 indicated by arrow B in place of the position indicated byarrow A, the resin can be more surely supplied to an area near theopening 26, where a larger number of ribs are formed and a larger amountof resin is required, as compared with when the recess 48 is formed in aposition remote from the opening 26 such as a position indicated byarrow C. When the gate is in the form of a valve gate, the whole recess48 may be a gate. In this case, the recess 48 may be made smaller sothat the gate mark becomes less remarkable.

Though the position of the gate when the upper half 2 is to beinjection-molded has been described, the gate for injection-molding thelower half 3 may be formed in a recess formed on the outer surface of athick wall portion positioned in the central portion of the bottom wall3A of the lower half 3 outside the circular opening 13.

In either of the upper or lower half, the gate may be formed in a recessformed for a purpose other than for providing a gate. For example, inthe case of the upper half 2 shown in FIG. 24, the gate may be formed ina position indicated by arrow D in a mark 49 which is a recess forindicating the direction in which the magnetic tape cartridge 1 is to beinserted into a recording and reproducing apparatus, or in a positionindicated by arrow E in a slip preventing recess 50. In the case of thelower half 3 shown in FIG. 26, the gate may be formed, for instance, ina gripping recess 51. Since these recess are inherently a recess forreasons of their function or design, use of the recesses eliminatesnecessity of forming an additional recess for positioning the gate.

Further, the gate may be formed in a position indicated by arrow F inone of the stacking recesses 12 of the upper half 2 shown in FIG. 24. Inthis case, it is preferred that the recess 12 be partly or entirelydeepened so that the gate mark does not interfere with the stackingprojection 11 inserted into the recess 12. The stacking projections 11and recesses 12 need not be limited to those of the illustrated shapebut may be, for instance, of a shape elongated in the direction ofinsertion of the cartridge casing 7.

As described above, the stacking projections 11 and recess 12 are formedon the lower half 3 and the upper half 2 so that, when a plurality ofmagnetic tape cartridges 1 are stacked, the stacking projections 11 onthe lower half 3 of an upper magnetic tape cartridge 1 is engaged withthe stacking recesses 12 on the upper half 2 of a lower magnetic tapecartridge 1 are engaged with each other to prevent the upper and lowermagnetic tape cartridges 1 from being displaced relative to each other.It is needless to say that the stacking projections 11 may be formed onthe upper half 2 with the stacking recesses 12 formed on the lower half3. In this case, the gate for injection molding of the lower half 3 maybe formed in one of the stacking recesses 12.

In the case where a pair of locator holes 33 for locating in place themagnetic tape cartridge 1 in the recording and reproducing apparatus areprovided on the lower half 3 of the cartridge casing 7, the gate may beprovided in a recess formed on the outer surface of the lower half 3 ina region 52 surrounded by a straight center line L4 which passes throughthe center of the lower half 3 in parallel to the straight line L3joining the locator holes 33 and a pair of straight lines L5 and L6extending on the outer surface of the lower half 3 through therespective locator holes 33 in perpendicular to the center line L4.

In this case, when the gate is provided in a recess formed on the outersurface of the lower half 3 at substantially the same distance from thelocator holes 33, or in the central portion of an area 53 joining thelocator holes 33 indicated by arrow G, the resin can be evenly suppliedto both the locator holes 33 from the gate and accordingly the locatorholes 33 can be formed at a high accuracy.

Further, the gate may be provided in a recess formed in the end face ofa projection 11 (the end face toward which the projection 11 projects)on the lower half 3, e.g., at a portion indicated by arrow H.

Further, the gate may be provided in a region 54 on the trailing side ofthe projections with respect to the direction of insertion of themagnetic tape cartridge 1 into the recording and reproducing apparatus.In this case, since the region 54 is not brought into contact with therecording and reproducing apparatus due to existence of the stackingprojections 11 when the magnetic tape cartridge 1 is moved in therecording and reproducing apparatus, the problems that the gate markleft on the surface of the product obstructs loading and unloading ofthe magnetic tape cartridge in and from the recording and reproducingapparatus and the gate mark is ground to produce plastic grindings canbe avoided without forming a recess.

FIGS. 27 to 31 are views for illustrating measures to preventdeformation of the cartridge casing 7 near a cutaway portion 60 forpreventing the magnetic tape cartridge 1 from being inserted into therecording and reproducing apparatus in a wrong direction. FIG. 27 is aperspective view of the cartridge casing 7, FIG. 28 is a bottom view ofthe corner of the upper half 2 where the measures are not taken, andFIGS. 29A and 29B are cross-sectional views respectively taken alonglines A—A and B—B in FIG. 28.

The structure where the measures are not taken and the problem inherentto the structure will be first described. The end of the arcuate rib 32,which is erected from the corner of the upper half 2 to surround thereel 4 (FIG. 1) for the magnetic tape 20, merges into the side wall 61of the upper half 2 in tangential directions of the rib 32 as shown inFIG. 28. Further, the corner of the upper half 2 is provided with acutaway portion 60, for preventing the magnetic tape cartridge 1 frombeing inserted into the recording and reproducing apparatus in a wrongdirection as shown in FIG. 27. The cutaway portion 60 is formed from theupper surface of the upper half 2 halfway of the height of the side wall61 by cutting the corner of the upper half 2 in a shape like a triangleincluding a point near the intersection of the arcuate rib 32 and theside wall 61.

In such a case, the part of the side wall 61 (indicated at P in FIG. 27)near the intersection forms a recess at an upper half thereof (a lowerhalf as viewed in FIGS. 29A and 29B) due to existence of the cutawayportion 60 while forming a thick wall portion 62 at a lower portionthereof as viewed in FIG. 29B.

The thick wall portion 62 is cooled slower than the surrounding parts,which results in a sinkmark and/or lean in the part of the side wall 61indicated at P and a step on the surface to be mated with thecorresponding part of the lower half 3 due to a difference in shrinkagefactor and the like.

In order to overcome this problem, a thickness reduction portion 63 isformed on the back side of the side wall 61 at a part above the cutawayportion 60 so that the part forms a thin wall portion 64 the wallthickness of which is substantially equal to that at the cutaway portion60 as shown in FIG. 30 and FIG. 31, which is a cross-sectional viewtaken along line B—B in FIG. 30.

In order to ensure dust-tightness, the butt end 61 a of the side wall 61of the upper half 2 to the side wall 65 of the lower half 3 forms asocket joint together with the butt end 65 a of the side wall 65 of thelower half 3 as shown in FIGS. 29B and 31. So the butt end 32 a of therib 32 of the upper half 2 to the rib (not shown) of the lower half 3is.

By thus forming a thickness reduction-portion 63 on the back side of aportion of the side wall 61 adjacent to the cutaway portion 60 in thedirection of height of the side wall 61, the difference in cooling ratenear the aforesaid intersection can be substantially nullified duringinjection molding, whereby formation of a sinkmark and/or lean in thepart near the intersection is prevented and formation of a step on thesurface at which the upper and lower halves 2 and 3 are mated isprevented.

Though, in the illustrated arrangement, the cutaway portion 60, forpreventing the magnetic tape cartridge 1 from being inserted into therecording and reproducing apparatus in a wrong direction, is formed onthe upper half 2, the same measures can be taken if the cutaway portion60 is formed on the lower half 3 halfway of the height of the side wallfrom the bottom surface of the lower half 3.

In addition, all of the contents of Japanese Patent Application Nos.10(1998)-133544, 10(1998)-149285, 10(1998)-158745, 10(1998)-176064 and10(1998)-219994 are incorporated into this specification by reference.

What is claimed is:
 1. A magnetic tape cartridge comprising a cartridgecasing formed of upper and lower halves fixed together by screws and asingle reel which is housed in the cartridge casing for rotation andaround which a magnetic tape is wound, a tape draw-out opening beingformed in the side wall of the cartridge casing, wherein the improvementcomprises that a first boss provided with a locator hole for locatingthe magnetic tape cartridge relative to a recording and reproducingapparatus when the magnetic tape cartridge is loaded in the recordingand reproducing apparatus and a second boss provided with a screw holethrough which a screw for fastening together the upper and lower halvesof the cartridge casing is inserted are erected in contact with eachother or close to each other from the inner surface of the cartridgecasing near the tape draw-out opening, and the wall thickness of thefirst boss is smaller than the wall thickness of the second boss.
 2. Amagnetic tape cartridge as defined in claim 1 in which the wallthickness of the first boss is in the range of 0.5 to 0.8 times the wallthickness of the second boss.
 3. A magnetic tape cartridge comprising acartridge casing formed of upper and lower halves fixed together byscrews and a single reel which is housed in the cartridge casing forrotation and around which a magnetic tape is wound, a tape draw-outopening being formed in the side wall of the cartridge casing and asliding door a sliding door being provided to open and, close the tapedraw-out opening, wherein the improvement comprises that a first bossprovided with a locator hole for locating the magnetic tape cartridgerelative to a recording and reproducing apparatus when the magnetic tapecartridge is loaded in the recording and reproducing apparatus and asecond boss provided with a screw hole through which a screw forfastening together the upper and lower halves of the cartridge casing isinserted are erected from the inner surface of the cartridge casing nearthe tape draw-out opening and the second boss is provided on the outerperipheral surface thereof with a flat surface which is in alignmentwith the inner edge of a sliding groove formed on the cartridge casingso that the sliding door slides on the groove.
 4. A magnetic tapecartridge as defined in claim 3 in which an arcuate rib coaxiallysurrounding the reel is erected from the inner surface of the cartridgecasing and the first and second bosses are erected apart from the rib.5. A magnetic tape cartridge comprising a cartridge casing formed ofupper and lower halves fixed together and a single reel which is housedin the cartridge casing for rotation and around which a magnetic tape iswound, a tape draw-out opening being formed in the side wall of thecartridge casing, wherein the improvement comprises that a boss providedwith a locator hole for locating the magnetic tape cartridge relative toa recording and reproducing apparatus when the magnetic tape cartridgeis loaded in the recording and reproducing apparatus is erected from theinner surface of the lower half of the cartridge casing near the tapedraw-out opening, and the inner surface of the upper half of thecartridge casing is provided with a circular recess opposed to the boss.